Mineralogénesis de sales sulfatadas-cloruradas magnésicas en la Laguna de Alcahozo (La Mancha-Ciudad Real)

Abstract

Alcahozo pond occupy the hydrographycally lowest area of a closed drainage bassin of 9 km2, near Pedro Munoz (La Mancha-Spain). Saline and mud deposits occupy only 0.94 km2. This pond may be classified as ephemeral saline lake, with a shalow body of concentrated brine. The brine is of S042- - Cl' - Na+ - Mg2+ type, and rise 180 g/1 in the winter, and the eutonic point, with bischofite precipitation in the summer. Direct rain fall (450 mm/year) and underflow (19 mm/year) are the most important origin of inflow water. Open water evaporation (1024 mm/year) exceed water inflow and it is the only condition which must be met to form the saline pond. Disolved salts are seasonally recycled, a scarce segregation of less soluble salts related with wind blow erosion of saline muds. Salt deposition in summer show a rim zoned distribution. The outer zone is occupied by a mud flat with eflorescent crust of gypsum - hexahydrite (epsomite) - (mirabilite) - halite. Between saline mud flat and salt pan there are a blister algal mat with a eflorescent crust of bischofite-mirabilite-gypsum and halite. Inner saline pan deposits are mainly formed by a saline crust (cm) of bischofite and minor hexahydrite and halite. Deposits of clastic sediments in the pond are only related with wind erosion. There are also microwindblown dunes of saline deposits in the inner saline pan. An approach to physico-chemical model of saline mineral paragenesis is proposed.